Direct Electron Transfer of Horseradish Peroxidase in Gellan Gum–Hydrophilic Ionic Liquid Gel Film

Abstract

Abstract A new composite film of microbial exocellular polysaccharide‐gellan gum (GG) and hydrophilic room temperature ionic liquid 1‐butyl‐3‐methyl‐imidazolium tetrafluoroborate (BMIMBF 4 ) was firstly used as an immobilization matrix to entrap horseradish peroxidase (HRP), and its properties were studied by UV/vis spectroscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The results showed that BMIMBF 4 could promote the electron transfer between HRP and electrode surface, and the existence of GG could successfully immobilize BMIMBF 4 on the electrode surface with improved stability. HRP–BMIMBF 4 –GG/GCE exhibited a pair of well‐defined and quasireversible cyclic voltammetric peaks in 0.1 M pH 7.0 phosphate buffer solutions at 1.8 V/s, which was the characteristic of HRP Fe(III)/Fe(II) redox couples. The formal potentials ( E °′) was −0.368 V (vs. SCE) and the peak‐to‐peak potential separation (Δ E P ) was 0.058 V. The peak currents were five times as large as those of HRP–GG/GCE. The average surface coverage ( Γ* ) and the apparent Michaelis‐Menten constant ( K m ) were 4.5×10 −9 mol/cm 2 and 0.67 μM, respectively. The electron transfer rate constant was estimated to be 15.8 s −1 . The proposed electrode showed excellent electrocatalytic activity towards hydrogen peroxide (H 2 O 2 ). The linear dynamic range for the detection of H 2 O 2 was 0.05–0.5 μM with a correlation coefficient of 0.9945 and the detection limit was estimated at about 0.02 μM ( S / N =3). BMIMBF 4 –GG composite film was promising to immobilize other redox enzymes or proteins and attain their direct electrochemistry.